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Thursday, December 18, 2014

White Fuzzies on Cactus Probably Cochineal Scale

Q. I planted a "cows tongue" or sometimes called "angel wing" cactus last spring and over the summer it began to develop some white cottony looking growth around each of the spines on the lower pads.  The white growth has continued and now covers much of the pads and some of the lower pads have actually fallen off. What is this white growth?  Is this a common problem with the cows tongue or is it common to all padded cacti and if so what can be done to rid the plant of the growth.  Someone had mentioned that it could be because of my watering schedule.  What do you think?
A. I don't have a picture of this problem on your cactus so I am following the KISS (Keep It Simple Stupid) diagnosis technique. The stupid part is to remind me that nine times out of 10 it is a common problem, not a rare event.

This is most likely problem is Cochineal scale, a common problems on cacti.
Heavy infestation of cochineal scale on Opuntia cactus.
If you touch it and it leaves a blood red liquid on your finger it is Cochineal scale. Both are scale insects hiding under that cottony growth and feeding on plant juices. When they reproduce and their populations increase, the feeding damage is so great it causes the plant or parts of the plant to collapse and ultimately die.
The red dye produced by cochineal scale when it is damaged. Notice how cochineal scale is commonly found close to the spines.
For either of these insects the control measures are the same. You can take a cotton swab and dab each of the cottony growths with alcohol or apply a systemic insecticide to the soil such as those containing imidicloprid so the poison will be taken up by the roots and moved to where this scale insect is feeding thus killing the insect.

The cochineal scale has an interesting history in Central America where this red extract was valued by Spanish colonizers as a dye until it was replaced by synthetic dyes. The actual insect was a very close relative of the Cochineal scale we see in our landscapes now. 

4 comments:

  1. I have 2 Huge prickly pear cactus totally loaded with this, they are both falling apart. I am concerned that with the hot temperatures (100 F +) if it is safe to do treatment.

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    1. Temperatures wont have an effect on treatment. POwer wash the pads with a sweep nozzle then follow up with an insecticide spray. If you only use a sweep nozzle it will be a weekly job.

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  2. Confused by your answer. You say it’s likely cochineal scale but then refer to “treatment is same for EITHER insects” and “BOTH are scale insects” but I only see you mention one insect (cochineal scale). What’s the second?

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    1. Thanks for pointing it out. It was awhile back when I wrote that and I don't remember exactly what was going through my mind except that my colleagues from the University of Sonora in Hermosillo told me that this scale insect (technically) is not the exact same insect the Spaniards were using for the dye. This cochineal scale insect is a close cousin to the actual cochineal scale that was used at the time. Both produce the scarlet dye but technically not the same insect. Same genus, different species. Treatment for control is the same. Just me being a bit anal about the explanation and wanting to be technically correct respecting the information they provided to me.

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